416 



D. R. Semmes — Tertiary Intrusives of 



about a thousand feet above the river. From the 

 "breaks" of the plains, or the cap-rock, to the foothills of 

 the mountains the Pecos Valley is approximately one hun- 

 dred miles in width. 



Stratigraphy. 



The following section represents the formations that 

 are to be found in the area under discussion, though the 

 entire section is not represented" in any one particular 

 locality. The two lowermost formations of the Pennsyl- 

 vanian underlie the series in the Rio Grande Valley, but 

 they are not exposed east of the divide and it is not cer- 

 tain that they are at all represented in the Pecos Valley. 



Fig. 1. — Map of a portion of Southeastern New Mexico. 



Age Formation Thickness Lithologic Character 



Recent Caliche 0-50 Surface layer of redissolved 



calcium carbonate, usually 

 conglomeratic with numerous 

 irregular limestone frag- 

 ments and some water worn 

 pebbles. Sometimes under- 

 lain by pebble beds and un- 

 consolidated sands. 



Tertiary (?) 10-40 Massive pebble conglome- 



rates, locally known as ' ' con- 

 crete. ' ' Usually found 



